A proposal to release genetically engineered mosquitoes in the Florida Keys to combat dengue and other tropical diseases has alarmed residents of the archipelago, many of whom packed a community meeting last week in Key West to express their concerns about the plan.

The U.K.-based company Oxitec is seeking permission from the federal government to introduce the modified mosquitoes in Key Haven next spring. Opponents, including several scientists, worry about the plan’s unintended consequences, which they say have not been fully studied. Oxitec officials insist that the technology is safe and effective.

“There are lots of questions that need to be answered,” said Mila de Mier, a local real estate agent and an opponent of the plan. “This is bigger than a couple people raising objections; the government is trying to do an experiment with the people of Florida.”

Under the proposal, which has been in development for more than three years, Oxitec would work with local mosquito-control officials—who support the idea—to introduce modifiedAedes aegypti mosquitoes, which can transmit dengue and chikungunya, into the environment.

The engineered insects carry a gene that will kill them unless they are fed the antibiotic tetracycline. Once male insects are released, they live long enough to mate with females, whose offspring die before maturing.

Opponents say there are no published, peer-reviewed studies to support Oxitec’s safety claims, and that the last case of dengue in the Keys were reported in 2010.

The Key West City Commission passed a resolution in 2012 opposing the plan, “until further research is provided and approved.” That same year, de Mier posted an online petition and hand-delivered the document, which has garnered more than 135,000 signatures, to the U.S. Food and Drug Administration, which must approve the proposal.

“I love technology, but it has to be safe,” de Mier said. “And besides, is there really a need for it now? Are we in a state of emergency? The concept is great, but I would like to see peer-reviewed studies.”

Opponents have several concerns. They contend that some offspring will survive into adulthood and worry that modified mosquitoes could pose a threat to bats that prey on mosquitoes. They also say that other disease-bearing mosquitoes might fill the void created in the absence of Aedes aegypti.

Critics also contend that Oxitec cannot completely sort mutated insects by gender, resulting in the release of biting females into the environment (male mosquitoes do not bite humans).

Oxitec spokesperson Chris Creese said dengue is caused by five different viruses or subtypes. “They are all transmitted by this species of mosquito,” she noted. “So yes, it is clear the virus will mutate. But if you can stop the mosquito, you can stop the disease.”

Creese added that under laboratory conditions, up to 5 percent of offspring survive to adulthood. “However in the open environment one has harsher conditions and we don’t see that level of survival,” she said. “We haven’t seen any survivors after a couple of weeks.”

Creese conceded that some female mosquitoes could be released, but Oxitec’s sorting technology has been 99 percent efficient. “We have been very open about this,” she said. “Getting bitten by an Oxitec female mosquito would be the same as getting bitten by a wild one.”

The genes introduced are nontoxic and nonallergenic, meaning they do not harm bats, she added.

As for peer-reviewed studies, Creese said that “the safety of the G.M. mosquitoes has been reviewed by regulatory agencies in Brazil, Malaysia, Cayman and Panama…and none of the agencies determined any [increased] risk to human health or the environment.”

Scientists are divided over the controversy.

Lawrence Gostin, a professor of global health law at Georgetown Law, said the technology could be beneficial. “We should not shun novel scientific ways to deal with urgent health problems,” he said in an email.

“The use of engineering in a biological context does not recognize the complexity of biological systems,” Bar-Yam said. “Over the past number of years, we’ve been doing stuff and then reacting to the consequences, and we’re in a situation where that kind of trial-and-error learning is extremely risky. Anything we do can cascade in quite uncontrolled ways.”

So, is it preferable to use harmful pesticides?

“Yes,” Bar-Yan said. “We should use technologies that don’t spread. Things that propagate by themselves, as biological modifications do, are more dangerous, fundamentally, than things that are essentially local.”

And, the scientist cautioned, “we may win the gamble a bunch of times, but it only takes once for there to be a huge impact for us to regret that we’ve ever done this.”

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